U.S. patent number 5,442,428 [Application Number 08/246,499] was granted by the patent office on 1995-08-15 for image recording apparatus.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Hideki Kamiyama, Katsuya Kawagoe, Yasunori Kawaishi, Toshiaki Motohashi, Mitsuru Takahashi, Hideo Yu.
United States Patent |
5,442,428 |
Takahashi , et al. |
August 15, 1995 |
Image recording apparatus
Abstract
An image recording apparatus is disclosed which includes an
intermediate transfer belt rotatable in a reciprocating motion.
Before the belt is rotated back and forth for forming a composite
toner image, it is rotated in the opposite direction to the image
forming direction. This provides the belt with substantially the
same deviation in both the forward movement and the reverse
movement. Hence, the apparatus insures desirable images by
preventing the individual toner images from being brought out of
register due to the deviation of the belt.
Inventors: |
Takahashi; Mitsuru (Tokyo,
JP), Kawaishi; Yasunori (Narashino, JP),
Yu; Hideo (Tokyo, JP), Motohashi; Toshiaki
(Tokyo, JP), Kawagoe; Katsuya (Kamakura,
JP), Kamiyama; Hideki (Yokohama, JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
|
Family
ID: |
14744233 |
Appl.
No.: |
08/246,499 |
Filed: |
May 20, 1994 |
Foreign Application Priority Data
|
|
|
|
|
May 20, 1993 [JP] |
|
|
5-118754 |
|
Current U.S.
Class: |
399/302;
399/301 |
Current CPC
Class: |
G03G
15/0131 (20130101); G03G 15/1605 (20130101) |
Current International
Class: |
G03G
15/16 (20060101); G03G 15/01 (20060101); G03G
013/16 () |
Field of
Search: |
;355/271-276,326R,327 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moses; R. L.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
What is claimed is:
1. An image recording apparatus comprising:
an image carrier for sequentially forming toner images of
respective colors on a surface thereof;
an intermediate transfer belt passed over a plurality of rollers
and rotatable in a reciprocating motion, said intermediate transfer
belt having guides at opposite edges thereof for being prevented
from deviating;
the toner images being transferred from said image carrier to said
intermediate transfer belt, which is in a reciprocation motion, one
above the other, and then a resulting composite toner image being
transferred to a recording medium;
said intermediate transfer belt being rotated, before sequential
transfer of the toner images to said intermediate transfer belt, in
a reverse direction opposite to a direction for image
formation.
2. An apparatus as claimed in claim 1, wherein said intermediate
transfer belt is caused to rotate at least one rotation, preferably
two or more rotations, in the reverse direction.
3. An apparatus as claimed in claim 1, wherein said intermediate
transfer belt is rotated in a forward direction after the rotation
in the reverse direction.
4. An apparatus as claimed in claim 3, wherein said intermediate
transfer belt is caused to rotate half a rotation to one rotation
in the forward direction.
5. An apparatus as claimed in claim 1, further comprising thrust
position sensing means for sensing a position of said intermediate
transfer belt in a thrust direction, whereby whether or not to
rotate said intermediate transfer belt in the reverse direction is
determined in response to an output of said thrust position sensing
means.
6. An apparatus as claimed in claim 5, wherein said belt thrust
position sensing means detects a faulty movement of said
intermediate transfer belt while sensing the position in the thrust
direction.
7. An apparatus as claimed in claim 6, further comprising alarming
means for alerting an operator to the faulty movement of said
intermediate transfer belt.
8. An apparatus as claimed in claim 1, further comprising control
means for controlling a duration or a number of times of rotations
of said intermediate transfer belt in the reverse direction on the
basis of a number of single color copies produced previously or a
number of forward rotations performed by said intermediate transfer
belt previously.
9. An apparatus as claimed in claim 1, wherein a movement of said
intermediate transfer belt occurs just after a copy start key has
been operated in a multicolor copy mode or after transfer of the
composite toner image to the recording medium or cleaning of said
intermediate transfer belt.
10. An apparatus as claimed in claim 1, wherein when two or more
copies each carrying the composite toner image thereon are to be
produced, said intermediate transfer belt is rotated in the forward
direction and the reverse direction a same number of times before a
start of forward rotation for the first color of each copy.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a color copier, color printer or
similar image recording apparatus and, more particularly, to an
image recording apparatus of the type having an image carrier, and
an intermediate transfer belt passed over rollers and provided with
guides to be prevented from deviating in position. In this type of
apparatus, toner images of respective colors are sequentially
formed on the image carrier and then transferred to the belt, which
is rotated in a reciprocating motion, and the resulting composite
toner image is transferred from the belt to a paper or similar
recording medium.
In the above-described type of image recording apparatus, the
intermediate transfer belt is generally rotated in opposite
directions in a reciprocating motion, as mentioned above, or only
in the forward direction for the transfer of the toner images from
the image carrier to the belt. The forward rotation scheme is such
that after the transfer of a toner image of first color to the
belt, the belt is continuously rotated in the forward direction, a
toner image of second color is transferred to belt with the leading
edge thereof in register with that of the toner image of first
color, and then toner images of third and fourth colors are
sequentially transferred to the belt in the same manner. On the
other hand, the reciprocation scheme is such that after the
transfer of the toner image of first color to the belt, the belt is
returned by the same distance as it moved in the forward direction
(during the return, the belt is spaced apart from the image
carrier), the toner image of second color is transferred to the
belt with the leading edge thereof in register with that of the
toner image of first color, and then toner images of third and
fourth colors are sequentially transferred to the belt in the same
manner.
Considering changes in the circumferential length of the belt, the
reciprocation scheme, which returns the belt the same distance by
use of a stepping motor or similar drive source, is advantageous
over the forward rotation scheme. It has been reported that the
belt deviates to either side due to, among others, the degree of
parallelism of rollers over which it is passed, and that the
deviation during forward movement and the deviation during reverse
movement are opposite in direction. It follows that the deviations
during forward movement and reverse movement are substantially
equal to each other. Therefore, the individual toner images
combined on the belt appear almost in accurate register.
However, assume an image recording apparatus having an intermediate
transfer belt which is provided with guides at opposite edges
thereof in order to be prevented from deviating to either side
while in rotation. The problem with this kind of apparatus is that
when the belt is continuously rotated in one direction, it is
prevented from deviating more than a predetermined amount by the
guides. When the reciprocation scheme is applied to such a belt,
the belt does not deviate during the formation of a toner image of
first color, i.e., while in forward rotation, due to the guides.
However, in the event of reverse rotation, the belt deviates in the
opposite direction noticeably. This is also true with the formation
of toner images of second, third and fourth colors although the
degree of deviation is reduced. As a result, the consecutive
deviations are summed up to result in a substantial total
deviation. Experiments showed that the total deviation of the belt
ranges from 0.3 mm to 1 min.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an
image recording apparatus which insures high quality images by
preventing individual images to be combined from being displaced
due to the deviation of an intermediate transfer belt.
An image recording apparatus of the present invention has an image
carrier for sequentially forming toner images of respective colors
on the surface thereof, and an intermediate transfer belt passed
over a plurality of rollers and rotatable in a reciprocating
motion. The intermediate transfer belt has guides at opposite edges
thereof for being prevented from deviating. The toner images are
transferred from the image carrier to the intermediate transfer
belt, which is in a reciprocation motion, one above the other, and
then the resulting composite toner image is transferred to a
recording medium. The intermediate transfer belt is rotated, before
the sequential transfer of the toner images to the intermediate
transfer belt, in a reverse direction opposite to a direction for
image formation.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present
invention will become more apparent from the following detailed
description taken with the accompanying drawings in which:
FIG. 1 is a section of an image recording apparatus embodying the
present invention;
FIG. 2 is an enlarged section of a photoconductive element included
in the embodiment, together with various units surrounding it;
FIG. 3 is a fragmentary perspective view of an intermediate
transfer belt also included in the embodiment;
FIG. 4 is a fragmentary perspective view of a guide adhered to the
belt;
FIG. 5 is a developed plan view indicative of a positional relation
between the belt and rollers over which it is passed;
FIG. 6 is a side elevation of the belt and rollers;
FIG. 7 is a graph representative of a relation between the
deviation of an intermediate transfer belt and the number of
rotations of the belt;
FIG. 8 is a graph representative of a relation between the
deviation of the belt and the number of rotations of the belt
particular to one embodiment of the present invention;
FIGS. 9A and 9B show the guides of the belt in a specific
condition;
FIG. 10 is a graph representative of a relation between the
deviation of the belt and the number of rotations of the belt
particular to an alternative embodiment of the present
invention;
FIG. 11 is a graph representative of a relation between the
deviation of the belt and the number of rotations of the belt for
the supplementary description of the behavior of the belt included
in the alternative embodiment; and
FIGS. 12A and 12B show a positional relation between the belt and
belt thrust position sensing means further included in the image
recording apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1 and 2, an image forming apparatus embodying
the present invention will be described which is implemented as a
color copier by way of example. As shown, the copier has a color
scanner, or color image reading device, 1, and optics including a
lamp 4, mirrors 5, and a lens 6. The color scanner 1 focuses an
image representative of a document 3 onto a color image sensor 7
via the optics, thereby reading blue (B), green (G) and red (R)
image data. Specifically, the image sensor 7 converts such optical
color components to corresponding electric signals. In the
illustrative embodiment, the color sensor 7 is implemented by B, G
and R color separating means and CCDs (Charge Coupled Devices) or
similar photoelectric transducers and capable of reading the three
colors B, G and R at a time. An image processing section, not
shown, performs color conversion on the basis of the intensity
levels of the B, G and R image signals generated by the color
scanner 1, thereby outputting black (BK), cyan (C), magenta (M) and
yellow (Y) color image data. A color printer 2 prints out the color
image data by use of BK, C, M and Y color toners so as to produce a
color copy.
To produce the BK, C, M and Y image data, the scanner 1 causes, on
receiving a scanner start signal synchronous to the operation of
the printer 2, the optics thereof to move in a direction indicated
by an arrow in FIG. 1. Every time the optics scans the document 3,
image data of one color is produced. As the optics scans the
document 3 four consecutive times in total, image data of four
colors are sequentially generated. The printer 2 sequentially forms
BK, C, M and Y images with toners of corresponding colors. The BK,
C, M and Y images are sequentially laid one upon the other to
complete a four-color or full color image.
Specifically, the printer 2 has an optical writing unit 8 for
converting the color image data from the scanner 1 to a
corresponding optical signal. The optical signal scans a
photoconductive drum 9 to electrostatically form a latent image
represented by the image data of particular color. The writing unit
8 includes a laser 8a, a laser driver, not shown, a polygon mirror
8b, a motor 8c for rotating the mirror 8b, an f-theta lens 8d, and
a mirror 8e.
As shown in FIG. 2, the drum 9 is rotatable counterclockwise.
Arranged around the drum 9 are a drum cleaning unit, including a
precleaning discharger, 10, a discharge lamp 11, a main charger 12,
a potential sensor 13, a BK developing unit 14, a C developing unit
15, an M developing unit 16, a Y developing unit 17, a reference
density pattern sensor 18, and an intermediate transfer belt 19.
The developing units 14, 15, 16 and 17 respectively accommodate
developing sleeves 14a, 15a, 16a and 17a, paddles 14b, 15b, 16b and
17b, and toner concentration sensors 14c, 15c, 16c and 17c. The
sleeves 14a-17a are each rotatable to bring a developer of
associated color deposited thereon into contact with the surface of
the drum 9, thereby developing a latent image formed on the drum 9.
The paddies 14b-17b are each rotatable to scoop up and agitate the
developer. The sensors 14c-17c are each responsive to the toner
concentration of the developer. In a stand-by condition, all the
developers deposited on the sleeves 14a-17a are held in an
inoperative condition. In the event of development, such developers
are sequentially brought to an operative condition according to a
predetermined color image forming order, e.g., in the order of BK,
C, M and Y. As a result, latent images formed on the drum 9 are
sequentially developed by the BK, C, M and Y developers or
toners.
In operation, on the start of a copying operation, or cycle, the
color scanner 1 starts reading BK image data at a predetermined
timing. Based on the BK image data, a laser beam starts forming a
BK latent image electrostatically. Before the leading edge of the
BK latent image arrives at a developing position assigned to the BK
developing unit 14, the sleeve 14a of the unit 14 is caused to
rotate to render the developer deposited thereon operative. As a
result, the BK latent image is sequentially developed by the BK
toner from the leading edge to the trailing edge. As soon as the
trailing edge of the BK latent image moves away from the developing
position, the developer on the sleeve 14a, i.e., the developing
unit 14 is rendered inoperative. The operation of the developing
unit 14 is completed at least before the leading edge of a C latent
image to follow reaches a developing position assigned to the C
developing unit 15. To render the developer on the sleeve 14a
inoperative, the rotation of the sleeve 14a is reversed.
A BK toner image formed on the drum 9 by the above procedure is
transferred from the drum 9 to the intermediate transfer belt 19
which is rotating in synchronism with and at the same speed as the
drum 9. Let the image transfer from the drum 9 to the belt 19 be
referred to as belt transfer for the sake of simplicity. To effect
the belt transfer, a predetermined bias voltage is applied to a
bias roller 20 while the drum 9 and belt 19 are held in contact.
The BK toner image and C, M and Y toner images to follow are
sequentially formed on the drum 9 and transferred to the belt 19
one above the other, thereby completing a four-color image. Then,
the four-color image is transferred from the belt 19 to a paper or
similar recording medium at a time. The specific construction and
operation of an intermediate transfer belt unit, including the belt
19, will be described later.
Regarding the drum 9, the BK imaging process is followed by a C
imaging process. Specifically, the scanner 1 starts reading C image
data at a predetermined timing. Based on the C image data, a laser
beam starts writing a C latent image on the drum 9
electrostatically. After the trailing edge of the BK latent image
has moved away from the developing position of the C developing
unit 15 and before the leading edge of the C latent image arrives
thereat, the sleeve 15a of the unit 15 starts rotating to render
the associated developer operative. In this condition, the
developing unit 15 develops the C latent image with the C toner.
After the trailing edge of the C latent image has moved away from
the developing position, the developer on the sleeve 14a, i.e., the
developing unit 15 is rendered inoperative immediately. The
operation of the C developing unit 15 is completed at least before
the leading edge of an M latent image to follow arrives at a
developing position which is assigned to the M developing unit
16.
Subsequently, an M and a Y imaging process are sequentially
executed in the same manner as the BK and C imaging processes. The
M and Y processes will not be described since they are identical
with the BK and C processes, regarding the steps of reading image
data, forming a latent image, and developing the latent image.
As shown in FIG. 2, in the intermediate transfer belt unit, the
belt 19 is passed over a drive roller 21, the previously mentioned
bias roller 20, and driven rollers which will be described. A
motor, not shown, is drivably connected to the drive roller 21.
Arranged around the belt 19 are a belt cleaning unit 22 for
removing toner images transferred to the belt 19, and a paper
transfer unit 23 for transferring the composite four-color toner
image from the belt 19 to a paper. The belt cleaning unit 22 has a
brush roller 22a, a rubber blade 22b, and a mechanism 22c for
moving the unit 22 into and out of contact with the belt 19. While
the second, third and fourth toner images are sequentially
transferred from the drum 9 to the belt 19 after the first or BK
image, the cleaning unit 22 is spaced apart from the belt 19 by the
mechanism 22c.
The paper transfer unit 23 has a bias roller 23a, a roller cleaning
blade 23b, and a mechanism 23c for moving the unit 23 into and out
of contact with the belt 19. Usually, the bias roller 23a is spaced
apart from the belt 19. When the four-color image should be
transferred from the belt 19 to a paper at a time, the mechanism
23c urges the paper transfer unit 23 against the belt 19. At the
same time, a bias voltage is applied to the bias roller 23a. As a
result, the composite image is transferred from the belt 19 to a
paper 24, FIG. 1.
As shown in FIG. 1, the paper 24 is fed by a pick-up roller 25 and
a registration roller pair 26 such that it meets the leading edge
of the composite image on the belt 19 at the paper transfer
position of the paper transfer unit 23.
In the illustrative embodiment, after the toner image of first
color, i.e., BK toner image has been transferred to the belt 19 up
to the trailing edge thereof, the belt 19 is driven by a
reciprocation or quick return system, as follows. As soon as the BK
toner image has been fully transferred to the belt 19, the belt 19
is brought out of contact with the drum 9, caused to stop rotating
(forward), and then reversed, i.e., returned in the opposite
direction at high speed. After the leading edge of the BK toner
image on the belt 19 has moved away from a predetermined belt
transfer position and further moved a predetermined distance, the
reverse rotation of the belt 19 is stopped. When the leading edge
of a C toner image on the drum 9 arrives at a predetermined
position close to, but short of, the belt transfer position, the
belt 19 is again caused to move forward and brought into contact
with the drum 9. The C toner image is, of course, transferred to
the belt 19 such that it is in accurate register with the BK toner
image. The above procedure is also repeated with an M toner image
and a Y toner image to complete a four-color belt transfer image.
After the belt transfer of the Y or last toner image, the belt 19
is continuously moved forward without being returned. As a result,
the composite toner image is transferred from the belt 19 to the
paper 24.
The paper 24 carrying the toner image thereon is conveyed to a
fixing unit 28 by a conveyor unit 27. The fixing unit 28 fixes the
toner image on the paper 24 with a heat roller and a press roller
28b. Then, the paper, or full color copy, 24 is driven out of the
copier to a tray 29, FIG. 1. After the paper transfer, the drum
cleaning unit 10, including a precleaning charger 10a, a brush
roller 10b and a rubber blade 10c, cleans the surface of the drum
9. Subsequently, the discharge lamp 11 dissipates charges remaining
on the drum 9. On the other hand, the belt cleaning unit 22 is
pressed against the belt 19 by the mechanism 22c to clean the
surface of the belt 19.
In a repeat copy mode, after the first Y (fourth color) imaging
process, a second BK (first color) imaging process is executed by
the scanner 1 and drum 9. After the transfer of the first full
color image from the belt 119 to the paper 24, the second BK toner
image is transferred to the area of the belt 19 which has been
cleaned by the belt cleaning unit 22. Subsequently, the second full
color image is produced on the belt 19 in the same manner as the
first full color image.
Paper cassettes 30, 31, 32 and 33, FIG. 1, are each loaded with a
stack of papers of particular size. When one of the paper cassettes
30-33 is selected on an operation panel, not shown, the papers are
sequentially fed from the cassette to the registration roller pair
26 at a predetermined timing. OHP (Over Head Projector) sheets and
relatively thick sheets are fed from a manual tray 34.
The foregoing description has concentrated on a four-color copy
mode. In a three- or two-color copy mode, the procedure described
above is repeated a number of times corresponding to the colors
selected and the desired number of copies. In a single color copy
mode, one of the developing units storing the developer of desired
color is continuously held in the operative condition, and the belt
19 is continuously driven forward at a constant speed in contact
with the drum 9. During the course of this mode, the belt cleaning
unit 22 is held in contact with the belt 19.
As shown in FIG. 3, a guide 19a in the form of a band is adhered to
each edge of the belt 19 in order to restrict the deviation of the
belt 19 while it is in rotation. As shown in FIG. 4 specifically,
the guide 19a is implemented by a rubber band having a rectangular
cross-section which is 5 mm wide (w) and 0.8 mm thick (t). The
hardness of the band 19a is A 70 as prescribed by JIS (Japanese
Industrial Standards). As shown in FIGS. 5 and 6, among the rollers
over which the belt 19 is passed, the rollers around which the belt
19 wraps in substantial amounts (e.g. drive roller 21 and driven
rollers 35 and 36) are respectively provided with stepped ends 21a,
35a and 36a. The opposite guides 19a of the belt 19 are nested in
the opposite stepped ends 21a, 35a and 36a. In the illustrative
embodiment, the stepped ends 21a-36a each has a height h ranging
from 1 mm to 1.5 mm.
While the belt 19 is rotated in one direction, it deviates to the
front side or the rear side, as indicated in FIG. 5 (direction
perpendicular to the sheet surface of FIG. 6). However, since the
guides 19a abut against the associated shoulders of the stepped
ends 21a-36a of the rollers 21-36, any further deviation is usually
prevented. As shown in FIG. 5, the belt 19 has a width A+.alpha.
which is about 1 mm broader than the width A of the rollers 21-36
as measured in the thrust direction.
How the belt 19 behaves during rotation will be described with
reference to FIG. 7. At the beginning of operation, the belt 19
rotates forward continuously and, therefore, deviates to one side
due to, among others, the degree of parallelism of the rollers
21-36. When the copier is operated to produce a four-color or full
color copy, the belt 19 deviates 0 mm (F.fwdarw.G) during forward
rotation for the first color. Subsequently, as the belt 19 is
reversed, or returned, it deviates noticeably away from the
restricting portions; the deviation was measured to be 0.24 mm
(G.fwdarw.H). During forward rotation for the second color, the
belt 19 was found deviated 0.17 mm (H.fwdarw.I). Presumably, why
the deviation during forward rotation for the second color is
smaller than the deviation during reverse rotation is as follows.
During forward rotation for the second color, the guide 19a partly
abut against the associated ends of the rollers to restrict the
deviation of the belt 19. As a result, the belt 19 fails to fully
return to the position G occurred during forward rotation for the
first color. The belt 19 repeats such displacements afterwards.
When a four-color image is completed on the belt 19, the deviation
of the belt 19 is about 0.34 mm. Subsequently, as the reciprocating
motion of the belt 19 is repeated, the deviation during forward
rotation and the deviation during reverse rotation begin to
coincide with each other.
A reference will be made to FIG. 8 for describing the behavior of
the belt 19 in accordance with the present invention. As shown, at
the beginning of operation, the belt 19 rotates forward
continuously and, therefore, deviates to one side, as in FIG. 7.
Subsequently, the belt 19 is reversed to move the guides 19a
sufficiently away from the associated restricting portions (stepped
ends of rollers). At this instant, the belt 19, theoretically,
should only perform a single rotation in the reverse direction so
long as the guide 19a does not deform. However, in accordance with
the present invention, the belt 1 is caused to perform two
rotations in the reverse direction. This is because the guides 19a
wave due to the limited precision of their adhesion to the belt 19,
as shown in FIGS. 9A and 9B.
As a four-color copying cycle begins, the belt 19 deviates 0.2 mm
during the above-stated preliminary reverse rotation (G.fwdarw.H)
and then deviates 0.26 mm during forward rotation for the first
color (H.fwdarw.I). Subsequently, the belt 19 deviates 0.2 mm
during reverse rotation for the first color (I.fwdarw.J) and again
deviates 0.2 mm during forward rotation for the second color
(J.fwdarw.K). In this way, the deviation of the belt 19 becomes
substantially stable. When a four-color image is completed on the
belt 19, the total deviation of the belt 19 is as small as 0.06 mm.
This contributes a great deal to the accurate register of colors
which is susceptible to the deviation of the belt 19.
In the illustrative embodiment, as the deviation of the belt 19 per
rotation increases, the deviation directly translates into a
displacement. It is, therefore, preferable to provide the rollers,
over which the belt 19 is passed, with accurate parallelism.
The two preliminary reverse rotations of the belt 19 was successful
to obtain favorable results, as described above. However, the
number of preliminary reverse rotations should preferably be three
or more when the guides 19a are easy to deform or when they wave
noticeably. Further, when the guides 19a are apt to get on the
rollers over the restricting portions or stepped ends due to the
repeated rotation of the belt 19 in one direction the number of
reverse rotations of the belt 19 should preferably be changed in
matching relation to the number of rotations of the belt 19 in one
direction. In this case, when the number of reverse rotations is
increased, it is preferable that the guides 19a be prevented from
abutting against the opposite restricting portions due to the
deviation of the belt 19.
FIG. 10 shows an alternative embodiment of the present invention in
which the belt 19 performs, before copying, three rotations in the
reverse direction and then one rotation in the forward direction.
This embodiment contemplates to obviate the difference between the
deviation of the belt 19 during preliminary reverser rotation
(G.fwdarw.H; 0.2 mm) and the deviation during forward rotation for
the first color (H.fwdarw.I; 0.26 mm), i.e., the total deviation of
0.06 min.
To begin with, a reference will be made to FIG. 11 for the
supplementary description of the behavior of the belt 19. As shown,
assume that as the belt 19 repeats forward rotation, it deviates
0.2 mm for each rotation. Then, the belt 19 also deviates
substantially 0.2 mm for each reverse rotation. However, after the
continuous forward rotation of the belt 19, the deviation during
the first reverse rotation is slightly greater than the deviation
during the second and successive reverse rotations. Such a behavior
of the belt 19 indicates that by rotating, before copying, the belt
19 three rotations in the reverse direction and then one rotation
in the forward direction, it is possible to substantially eliminate
the deviation of the belt 19 when a four-color image is completed,
although some error occurs each time.
In summary, it will be seen that the present invention provides an
image recording apparatus having various unprecedented advantages,
as enumerated below.
(1) Before the reciprocation of the belt 19 for belt transfer, the
belt 19 is rotated in the opposite direction to the image forming
direction to insure accurate register of individual color
components.
(2) The belt 19 performs, at such a preliminary stage, at least one
rotation, preferably two or more rotations, in the reverse
direction. This further promotes accurate register of color
components.
(3) The duration or the number of rotations of the belt 19 in the
preliminary stage is controlled on the basis of the number of
single color copies produced before previously or the number of
forward rotations performed by the belt 19 previously. As a result,
an accurately registered full color image is achievable without
regard to various conditions, including getting on the belt rollers
and waving.
(4) After the preliminary reverse rotation, the belt 19 is rotated
forward to provide the resulting image with higher quality.
(5) To achieve the above advantage (4), half a rotation to one
rotation in the forward direction suffices.
(6) As shown in FIGS. 12A and 12B, a sensor, or belt thrust sensing
means, 37 may be used to sense the position of the belt 19 in the
thrust direction. Then, whether or not to reverse the belt 19,
i.e., whether or not both guides 19a are in contact with the
associated restricting portions is determined on the basis of the
output of the sensor 37. Further, the guides 19a can be moved away
from the associated restricting portions efficiently and
accurately. This is also successful in producing high quality
images.
(7) The preliminary movement of the belt 19 occurs just after the
operation of a copy start key in a multicolor copy mode or after
the transfer of a toner image to a paper or the cleaning of the
belt 19. Hence, it is possible to effect the preliminary operation
of the belt 19 efficiently without reducing the number of copies
per minute (CPM), i.e., by using an interval during which the belt
19 does not directly join in image formation. Such an interval is
available when, for example, a document is being read, when a
latent image is being developed, or when the paper 24 is being
driven out of the copier.
(8) When two or more multicolor copies are to be produced
continuously, the belt 19 is rotated forward and reversed the same
number of times before the start of forward rotation for the first
color of each copy. In this condition, the individual toner images
can be accurately superposed one above the other while the guides
19a are spaced apart from the associated restricting portions.
(9) The sensor 37 senses not only the position of the belt 19 in
the thrust direction, but also the faulty movement of the belt 19.
Alarming means, not shown, alerts the operator to the faulty
movement of the belt. This obviates defective images as would occur
when the belt fails to fully return even after the predetermined
number of rotations, the breakage of the belt 19, etc. In addition,
the sensor 37, serving as belt thrust position sensing means and
belt fault detecting means at the same time, reduces the cost of
the apparatus.
Various modifications will become possible for those skilled in the
art after receiving the teachings of the present disclosure without
departing from the scope thereof.
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